Recycling of paper

Conservation & RecycZing, Vol.1, pp.129-136.

Pergaman Press, 1976. Printed in Great Britain.

RECYCLING OF PAPER

F. J. COLON Centraal Technisch Instituut TNO, Apeldoorn,

Holland

Abstract-The market situation of paper and of the raw materials for paper production are reviewed, and it is concluded that, in the future, a shortage of raw materials is very probable. An additional source of fibres might be found in municipal refuse if appropriate processes can be developed. After a short descnption of the manufacture of paper, the physical basis of separation processes is outlined. The principle of the Zig Zag Air Classifier, an important part of the TN0 municipal refuse separation system, is discussed. Some of the results from the system, which is currently undergoing scaling up to lSt/h, will be shown.

INTRODUCTION The paper industry plays an important role in two fields of the world’s community. On the one hand it supplies the materials that are needed for the transport of the thoughts of human beings. On the other hand, it provides the materials needed for the protection of all sorts of goods that must be transported from one place to another. The demand for paper and paper products is directly related to the level of inter-human relations. As the development of a nation proceeds, the consumption of paper increases. The paper industry fulfils the demand by converting raw materials into the various paper products. Long ago, textile wastes were the main source of tibres. As there were not enough fibres available, the use of the other cellulose fibres, mainly derived from wood, was developed. The use of waste paper became common practice. Since the demand for paper is still rising, other sources of fibres must be exploited. One possible source is municipal refuse, if one could separate the fibres from the other wastes. For this reason the Dutch Research Organisation TN0 started an investigation into the application of industrial separation processes to separate paper from municipal waste. In the next section, some of the results of that investigation will be given and discussed.

THE MARKET SITUATION

OF PAPER FIBRES

The demand for paper is determinded to a large extent by the degree of industrial development of a country, as demonstrated by Fig. 1. If world consumption were based on the U.S.A. figures, the normal world resources of fibres would not be able to supply nearly enough material. The present structure of raw materials supply for the paper industry varies from country to country, depending on its natural wood resources. In Holland, which is short of wood, a high percentage of waste paper is used. The difference in the use of waste paper in various countries is demonstrated by Fig. 3. The growth of the paper market in the future might be influenced by the development of artificial fibres or sheets of plastics or by other communication methods such as audio visual aids, but it is very difficult to predict the development possibilities in that particular area. Figure 4 demonstrates how the paper market is expected to grow in the Netherlands, assuming that changes in the relation of new communication techniques to paper tibres may be neglected. The possibilities to meet the growing demand for paper tibres are: 1. Reduce the loss of paper. 129

F. J. COLON

130 paper

consumption

per capita

in 1972

in USA Sweden Canada Danmark Switserland Finlend Netherlands W.Germany Great Britain Australia

J-n hWW Wrm Now Zealand France Austria h&and Iceland D.D.fI. Italia

279 193 166 151 144 140 137 129,Q 128,Q 124,8 123,8 123 118 112 104.7

sources of raw materials for the pa(#r

8691 84,4 82 72,2 68

Fig. 1. Paper and cardboard consumption per capita in 1912.

production

Qround wood semi - chemiil

i

char&al

celluloss

cellulose

linters

straw I bagasss waste paper

Fig. 2. Sources of raw materials for paper and cardboard production.

Switserland 8RD 8elgium Gr. Britain France Spain Sweden ltalia USA Danmark Norway Finland Canada

Fig. 3. Collection of waste paper as percentage of paper and cardboard production in 1969.

2. Promote the collection of waste paper from industry traders and organisations such as the Boy Scouts. 3. Separate paper from municipal refuse. THE PRODUCTION

and trade centres by waste paper

OF PAPER

Paper is made by suspending fibres in water at a fibre concentration of ca. 0.3% (Fig. 5). The suspension is fed on to an endless cloth of a continuous paper machine where the water is drained and

131

RECYCLING OF PAPER

Fig. 4. Paper and cardboard production and raw materials supply in Holland,

water

I _

I leaf

-

forming

drying

_

cutting

paper

.

product

1 internal

waste

Fig. 5. Simplified flow-sheet of a production of paper and cardboard.

.

waste primary

secondary

Pubr

pulper

?? rejects

sieves

+

+ rejects

rejects

rejects

Fig. 6. Flow-sheet of stock preparation using waste paper.

the leaf is formed. The leaf is transported to a drying section where, by means of steam heated drums, it is dried. At the end of the machine the leaf is collected on a roll or cut into sheets. When waste paper is used as the raw material the preparation of the suspensio? takes place in a series of processes as indicated in (Fig. 6). In the pulper, a round tank of lo-15 m3-capacity, the fibres are freed from the paper structure in water by a mixing rotor. At the bottom of the tank is a perforated sieve plate to reject the coarse material. The pulping is repeated in a second pulper of a different construction. Higher shear rates and finer sieves are applied. The resultant pulp is cleaned by passing it through hydrocyclones and sieves (Fig. 7). Sand, dirt and tine tibres are rejected. into the pulper is shown in (Fig. 8).

A view

132

F. J. COLON

Fig. 7. Hydrocyclone.

Fig. 8 View inside pulper.

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OF PAPER

133

ADDITIONAL FIBRE SUPPLIES FROM WASTES In order to use the paper content of domestic refuse, it is necessary to develop processes to separate the paper from the other wastes. In the past, hand picking of paper from waste was sometimes practised, but hygiene and labour costs make this impractical nowadays. Separation systems The separation systems described in the literature may be divided into two groups: - separation of tibres after mixing up domestic waste with water _ separation without water addition. A wet separation system is under development by Black Clawson Co. [I] , who have constructed a semi-industrial plant at Franklin, OH, U.S.A. The Black Clawson process is based on the paper production process. Instead of cellulose, however, the pulper is fed with domestic waste. Of course the greater part is unusable and has to be drained. The disadvantage is the difficult processing of these wet waste residues. Moreover it creates a large quantity of waste water. The dry separation systems in development are based on separation by means of air separators, ballistics, screens or a combination of these. Piloting is going on, for instance, at: Stanford University, U.S.A. (2) Bureau of Mines, Pittsburgh (3) Forest Products Laboratory, Madison, U.S.A. (4) Franklin Institute, Philadelphia, U.S.A. (5). It is concluded from available information that in the Netherlands the ‘dry system’, both environmentally and economically, has good prospects. Without further work, the application of American data to Dutch waste is impossible. The composition of American domestic waste completely differs from Dutch waste. For instance, it contains almost twice as much paper as that in the Netherlands. Extensive examination of dry separation methods with normal Dutch domestic waste seemed to be desirable.

Separation

PHYSICAL PRINCIPLES OF SEPARATION PROCESSES processes in waste technology are mainly based on the following properties:

1. Magnetism 2. Falling velocity 3. Density 4. Particle size 5. Conductivity 6. Reflectivity. In the case of paper, separation properties 2, 3 and 4 are of importance. Two unit operations are mainly involved-sieve machines and air/water classifiers. In the sieve machine the size of the particles is the dominant parameter. The classifiers are based on the difference in falling velocity of the particles. In theory, falling velocity _-

Am

&

’ 1877 where Ap = difference in density of particle and medium g = acceleration due to gravity 7) = viscosity of the medium d = particle size. This is Stokes Law. In practice, however, with waste materials separations, the definitions of the characteristic size and density are impossible so experiments must be made to determine the separation conditions. I’--

134

F. J. COLON

Principle of the TN0 separation system Based upon present knowledge of separation techniques, complete with data from literature, TN0 studied the possibilities of a dry system for domestic waste. During the sepaiation of the mixture containing different materials present in domestic waste, the differences in physical properties of the materials are utilised. This system is shown in (Fig. 9). domestic *

non

grindable

f zigzag classifier

I

I heavy as

I waste

sand,

fine

non-ferro,

wood.

massif

plastics II

H

waste

mainly

glass

stone,

zigzag classifier

sieving machine

of organic

baler

nature plastic

I paper

Fig. 9. Flow diagram of TN0 separation system

F

G

Fig. 10. Principle of the zig-zag classifier. Primary separation of paper and residue waste is possible by shredding the waste, in the right way, into pieces of about 1Ocm in size. The paper achieves a different velocity by the size reduction of the remaining waste components. Separation based upon falling velocity is executed in a zig zag classifier (Fig. 10). The mixture to be separated using velocity is fed into a vertical channel, provided with a

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OF PAPER

number of bends. Air is blown up the channel with a fixed velocity. Small particles (F) are carried up by the air current, heavy particles (G) falling down along the wall. On the bend, the heavy waste crosses the air current, causing a separation once more. The quality of separation can be raised by using more channel units similar to the plates of a fractionating column. In 1932, Stebbins in the U.S.A. took out a patent of this type of unit. When supplying shredded waste to a well-designed classifier, paper leaves the classifier at the top together with the air current. This paper fraction still contains plastic films and fine waste. By screening and sifting a paper product is obtained which has possibilities as a raw material for the paper industry. State of development of the TN0 system In 1972, a preexamination at laboratory scale took place at the Central Technical Institute TNO. By means of a plant with a capacity of lOOkg/h domestic waste, a paper product was separated and the Fibre Institute produced experimental paper sheets. The cardboard industry considered the

Fig. 11. Zig-zag classifier

of it/h

capacity.

quality of the fibres as usable for cardboard production. Then a pilot plant with a capacity of It/h was designed and built. Figure 11 gives an impression of the Classifier 1 of that plant. The pilot plant has been built in the Municipal Waste Disposal Rlant at Haarlem. The city of Haarlem has shredded refuse for composting purposes since 1967, and has a total capacity of 50 000 t/a. The pilot plant was fed with a part of the refuse directly after the shredder (GONDARD).

136

F. J. COLON

After an investigation period of about six months, experiments have ended and the design of a separation plant with 15t/h capacity started, with completion expected by mid 1976. SOME RESULTS OF THE PILOT PLANT STUDY The separation of the Haarlem waste resulted in: 3% iron 25-3 5% heavy fraction 25-35% fine fraction 20-30% paper 5% plastic. A study concerning the economics of the process is being carried out by the Dutch Institute for Waste Disposal and the results will be published in the future. Some 4 tonnes of the paper product were transported to a paper machine factory, and there processed in the same way that mixed waste paper is normally processed. Figure 12 gives a flow sheet of that system. The difference from a normal stock preparation system is that the pulp is thickened on a drum type filter to ca. 70% wt. moisture and heated to 100°C. This is done for two reasons; homogenistation of waxy contaminants and killing of pathogens. The results of this experiment were such that it was decided to build the 15t/h plant and to carry out an evaluation of the paper product in a smaIl cardboard factory. Acknowledgement-The author wishes to acknowledge the help given by Ir. G. H. van Dorth of the Dutch Fibre Institute TN0 in connection with the details of paper production. REFERENCES 1. 2. 3. 4.

W. Herbert, TAPPI, 54 (lo), 1661-1663. A. Boettcher, ASME-PUBL. 69-WA/PID-9 (1969). C. B. Kenahan. Bureau of Mines Inf. Circ. No. 8529 (1971). W. F. Carr,P& TradeJ. 17,48-52 (1971). 5. Franklin Institute Research Labs. No. l-2911-02 (Rev. 1).